Datasheet

© 2009 Microchip Technology Inc. DS70175H-page 111
PIC24HJXXXGPX06/X08/X10
8.0 DIRECT MEMORY ACCESS
(DMA)
Direct Memory Access (DMA) is a very efficient
mechanism of copying data between peripheral SFRs
(e.g., UART Receive register, Input Capture 1 buffer),
and buffers or variables stored in RAM, with minimal
CPU intervention. The DMA controller can
automatically copy entire blocks of data without
requiring the user software to read or write the
peripheral Special Function Registers (SFRs) every
time a peripheral interrupt occurs. The DMA controller
uses a dedicated bus for data transfers and, therefore,
does not steal cycles from the code execution flow of
the CPU. To exploit the DMA capability, the
corresponding user buffers or variables must be
located in DMA RAM.
The PIC24HJXXXGPX06/X08/X10 peripherals that
can utilize DMA are listed in Table 8-1 along with their
associated Interrupt Request (IRQ) numbers.
TABLE 8-1: PERIPHERALS WITH DMA
SUPPORT
The DMA controller features eight identical data
transfer channels.
Each channel has its own set of control and status
registers. Each DMA channel can be configured to
copy data either from buffers stored in dual port DMA
RAM to peripheral SFRs, or from peripheral SFRs to
buffers in DMA RAM.
The DMA controller supports the following features:
• Word or byte sized data transfers.
• Transfers from peripheral to DMA RAM or DMA
RAM to peripheral.
• Indirect Addressing of DMA RAM locations with or
without automatic post-increment.
• Peripheral Indirect Addressing – In some periph-
erals, the DMA RAM read/write addresses may
be partially derived from the peripheral.
• One-Shot Block Transfers – Terminating DMA
transfer after one block transfer.
• Continuous Block Transfers – Reloading DMA
RAM buffer start address after every block
transfer is complete.
• Ping-Pong Mode – Switching between two DMA
RAM start addresses between successive block
transfers, thereby filling two buffers alternately.
• Automatic or manual initiation of block transfers
• Each channel can select from 19 possible
sources of data sources or destinations.
For each DMA channel, a DMA interrupt request is
generated when a block transfer is complete.
Alternatively, an interrupt can be generated when half of
the block has been filled.
Note: This data sheet summarizes the features
of the PIC24HJXXXGPX06/X08/X10 fam-
ily of devices. However, it is not intended
to be a comprehensive reference source.
To complement the information in this data
sheet, refer to the “PIC24H Family Refer-
ence Manual”, Section 22. “Direct Mem-
ory Access (DMA)” (DS70223), which is
available from the Microchip website
(www.microchip.com).
Peripheral IRQ Number
INT0 0
Input Capture 1 1
Input Capture 2 5
Output Compare 1 2
Output Compare 2 6
Timer2 7
Timer3 8
SPI1 10
SPI2 33
UART1 Reception 11
UART1 Transmission 12
UART2 Reception 30
UART2 Transmission 31
ADC1 13
ADC2 21
ECAN1 Reception 34
ECAN1 Transmission 70
ECAN2 Reception 55
ECAN2 Transmission 71